Dear Mengistu,

Check this out:

Conceptual and methodological issues relevant to cytokine and inflammatory marker measurements in clinical research

Xin Zhou, et al. Curr Opin Clin Nutr Metab Care. Sep 2010; 13(5): 541–547. 

"Historically, enzyme-linked immunosorbent assays (ELISAs) became the gold standard, yet this approach of measuring a single protein in each sample limits the amount of information which can be obtained from limited amounts of human sample. In recent years, commercially available multiplex technologies which detect large numbers of proteins in a limited volume have provided investigators with opportunities to begin addressing the complexity of inflammatory responses."

Drug-specific in vitro release of IL-2, IL-5, IL-13 and IFN-c inpatients with delayed-type drug hypersensitivity. P. Lochmatter et al. Allergy 2009: 64: 1269–1278

Flow cytometry is the most valuable curent technique for the determination of MDSCs. One must be careful with the cell subsets (such as MDSCs) which are funclionally distinguished since the surface markers cannot directly indicate functional state (there are certain non-MDSC cell types that can be stained with MDSC markers). Its better to accompany immunophenotyping with certain functional assays (i.e. for MDSCs, suppression of T cell activation/proliferation). And for chemokines, i agree with Béatrice Marianne Ewalds-Kvist, ELISA from serum samples obtained simultaneously at the time of MDSC analysis.

I would recommend flow cytometry backed up with ELISA. There are several papers describing how to perorm-

If your lab has multiplex or luminous it is better other wise ELISA. The different here is the quality and quantity of sample used. ELISA is little bit of different from the other.